During the last 20 years analogue high frequency repeaters in digital communication systems have been neglected in favour of digital solutions. Analogue amplifiers may be realized with analogue or digital signal processing methods and are characterized by foremost being completely or partly transparent. They give an amplified, analog representation of the input signal which offers a near unchanged bandwidth and very low latency even with very large system bandwidths Digital repeaters are not transparent and are likely to be based on just on type of modulation and one type of communication protocol which again is likely to be of proprietary character. The resulting conversion taking place within them gives a high current draw and usually they exhibit large physical dimensions. In addition each repeater contributes to a substantial reduction of total bandwidth of the system and introduces always problematic latencies that either excludes or complicates certain modern, time critical digital telecommunication services.
There will also be physical limits for how far technologies using digital repeaters can be developed for large bandwidths. Using semiconductors of known kinds there are physical limitations for how much it is possible to reduce power consumption at high processing speeds which among other is given by the lower limit for the transistor supply voltage and clock frequencies. Adding to this is that such solutions are not inexpensive to manufacture from for instance the need to always being obliged to use the latest and most expensive technology. Such technologies are therefore rapidly superseded by new generations resulting in high write-off costs. As a consequence it is therefore expensive and impractical to use sufficient number of such repeaters as for example to sustain low signal levels on cables or cover an area by wireless where line of sight obstructions are eminent. There is therefore a significant need for innovative solutions that give repeaters that can be used in larger numbers showing low production costs and that exhibit small dimensions and consume small currents. An analog repeater system can additionally be made compatible with any existing none proprietary communication system and will be usable with most future ones.
Analog repeaters do not have the drawbacks mentioned with respect to digital repeaters. It has been claimed that the main disadvantage of analog repeaters is their accumulation of noise. This conclusion contains substantial errors, besides it is a fact that a system with digital repeaters will accumulate noise that gradually reduce the symbol bandwidth in addition to the reduction of bandwidth happening due to the time delays associated with each repeater. It is know from old time's analog repeaters of telephone systems that they accomplished relaying the signals around the globe. With regenerative, super regenerative and super heterodyne analog repeaters it is possible to obtain regeneration of the signal that among other reasons is due to the averaging of noise in the same way as when amplifiers are connected in parallel. The accumulated, systematic noise may be reduced by various means. A large number of analog repeaters can be utilized until a significant degeneration of the signal takes place provided the repeaters have measures accordingly construction wise. The advantage of analog repeaters is that they consume substantially less energy than the digital. This is particularly important when they are to be battery powered or are to live off currents in conductors which they are loosely connected to, for example inductively.
I repeater or transponder systems as given in patent documents NO2001057, NO20010132, NO20040112, PCT/NO01/00079, PCT/NO003/00004N NO20040110, PCT/NO20050013 is shown how analog repeaters and systems using analog repeaters can be realized in sub optimal cases for both wireless and wire bound solutions or integrations of such. Characteristics for such impaired cases are when conventional schemes are not applicable or when sufficient isolation between input signal and output signal is not inherently increasable to become larger than the gain of the repeater. Consequently it is also characteristic of such cases that there are points along the signal medium where analog gain is necessary but where it is impractical to introduce such isolation. Examples of this are cable junctions that cannot be broken such as with power grid wires and cables. One example in wireless applications is when only one antenna can be applied or when large separation in the form of number of wavelengths cannot be realized. Further examples of unfavourable cases are when the isolation between input and output signals are reduced due to reflections of various causes. This may be the case for both wire bound and wireless systems. In wire bound systems a certain control may usually be exercises accordingly. In wireless systems variable reflection conditions if often a greater problem. A one port amplifier, meaning a repeater is stable only as long as sufficient isolation between the amplifier or repeater and a reflection occurring in the system or repeater cascade is present. It is therefore a need of novel, simple solutions that makes it more practical to meet such challenges. In some cases conventional principles have utilized circulators to aid isolation and achieve directional sensitivity. However, this is costly and additionally impractical in large numbers. Even other types of directional sensitivity is often impractical to implement.
The results of lacking isolation between input and output signals with signal repetition using frequency transposing is duplex noise.
The consequences under the mentioned impaired conditions followed by improper isolation or reflections may be that stability criteria for same channel signal repetition cannot be met.
When frequency transposing is applied in analog repeater systems it is often important that a minimum of channels are utilized for duplex purposes both to achieve the largest possible effective symbol bandwidth using the available frequency spectrum as well as to allow space for channels for two way communication or multiple channel systems to accomplish an increased, available system bandwidth. In this context it is also required to place adjacent channels as close to each other as possible. Super regenerative frequency converts allow very small spacing between input and output channel in a repeater as depicted in the publications NO20011057, NO20010132, NO20020112, NO20040110, PCT/NO01/00079, PCT/NO03/00004, PCT/NO20050013. There is a need for novel applications that can make more efficient use of available and useful channels in such systems. This is especially important in broad band applications. It is also particularly important in wireless applications when the density in certain frequency bands is large. It may be even more important in cable based systems, in particular with cables exhibiting poor high frequency properties where often only marginal frequency regions are available for the symbol bandwidth in demand today and in the future.
When the signal gain is larger than 1 for a same frequency repeater the stability criteria are important in order to utilize the gain. Reflections and echoes from other repeaters play a substantial role in order to achieve stability. The phase is influenced by the complex impedance the gain port or ports look into and by the isolation between the ports of a multi port gain block. Analog gains has to a large extent been omitted in modern networks due to the difficulties of achieving the combination of stability with sufficient gain. It is particularly difficult to produce solutions that are repeatable and possibly reproducible I large numbers or in large systems. Directional attenuation in some form is often the only and the best measure against echoes and reflections. In some applications attenuation of interference of 10 to 20 dB is sufficient, however in other applications that demand good linearity as with QAM and OFDM attenuations of 30 to 50 dB is required. For some modulation types problems with frequency beating may occur even with relatively large isolation. Previously published solutions are not capable of satisfying isolation levels and those principles only have limited applications as for instance with none linear systems like frequency modulation using rather narrow bandwidths. It is therefore a large need for novel, practical solutions that offer repeater stability combined with satisfactory gain and signal to noise ratio. There is a need for such solutions both for signal repetition using frequency transposing as well as same frequency repetition.
There is a large need for improvement of connectivity and installation friendliness in broad band systems utilizing the power grid as infrastructure generally. This need also concerns such systems that incorporate analog repeater systems.